1. Field
A backlight unit that is increases brightness and increases uniformity of the brightness is provided.
2. Related Art
Conventionally, there has been an increased trend in using liquid crystal display devices because of the appealing characteristics, such as lightness, thinness, low driving power consumption, etc. The liquid crystal display device has been used in office automation equipment, audio/video equipment, etc. The liquid crystal display device controls the transmitted amount of a light beam in accordance with a signal applied to a plurality of control switches that are arranged in a matrix shape, thereby displaying a desired picture on a screen.
The liquid crystal display device is not a self luminous display device, it requires a separate light source such as a backlight.
The backlight unit is classified as a direct type or an edge type in accordance with the location of a light source. The edge type backlight has a light source installed at the edge of one side of a liquid crystal display device and irradiates an incident light from the light source to a liquid crystal display panel through a light guide panel and a plurality of optical sheets. The direct type backlight has a plurality of light sources disposed right under the liquid crystal display device and irradiates the incident light from the light sources to the liquid crystal display panel through a diffusion plate and a plurality of optical sheets.
FIG. 1 represents one example of a backlight unit adopting LED (light emitting diode).
Referring to FIG. 1, a backlight unit of the related art includes a plurality of LED's 11 acting as point light source; and a light guide panel which converts light from the LED's 11 into a surface light to irradiate to a liquid crystal display panel.
The backlight unit, as shown in FIG. 1, has brightness that appears higher where the lights incident from the LED's 11 to a light guide panel 12 cross than in other parts of the guide. A bright spot occurs where the light from the different LED's 11 cross in the light guide panel 12. The bright spot appears in the shape of a ring, circle or ellipse, and is known as a “hot spot” in accordance with the shape. Due to this phenomenon, in the backlight unit and the liquid crystal display device of the related art, the brightness of the display picture is non-uniform because part of the guide panel 12 appears to be brighter in the display picture. FIG. 2 is a result of measuring the brightness on the light guide panel in the backlight unit as in FIG. 1. In FIG. 2, the brightest part, which is labeled the “HOT SPOT,” corresponds to the part 13, in FIG. 1, where the light from the different LED's 11 cross paths in the light guide panel 11.